There's obviously some symbolism I'm missing here...

Today I gave blood - no biggie, I do it as often as they're happy to take it. Except that it's apparently the third time I've given blood in a year (about my average), so this time they gave me a gift.

Now I'm trying to figure out why they think that a small slate coaster, about 3" wide, is especially appropriate as a gift. Yes, it has their logo on the front, and a label on the back saying it's made from slate umpty million years old. And it's quite nicely made, I suppose. But why a coaster?

I can only think that it's meant to go with the coffee mug they gave me a few years back. To be honest, another mug would be more useful...